Encapsulation by spray drying of bioactive components, physicochemical and morphological properties from purple sweet potato Maruf Ahmed a, b , Mst. Sorifa Akter a , Jin-Cheol Lee c , Jong-Bang Eun a, * a Department of Food Science and Technology, Institute of Biotechnology, Chonnam National University, 77 Yongbong-ro Buk-gu, Gwangju, 500-757, South Korea b Department of Food Processing and Preservation, Hajee Mohammad Danesh Science and Technology University, Dinajpur, Bangladesh c Biotechnology Industrialization Center, Dongshin University, South Korea article info Article history: Received 16 December 2009 Received in revised form 14 May 2010 Accepted 14 May 2010 Keywords: Spray-drying Sweet potato Maltodextrin Ascorbic acid Antioxidant capacity abstract Purple-fleshed sweet potato flour could be used to enhance the colour, flavour and nutrients in food products. Thus, the investigation was to produce encapsulated flours from purple-fleshed sweet potato by spray drying using combinations of various levels of ascorbic acid (5 g kg 1 and 10 g kg 1 ) and maltodextrin (30 g kg 1 and 100 g kg 1 ) and to evaluate their effects on bioactive components, physicochemical and morphological properties. Encapsulated flours had higher total phenolic content, antioxidant capacity and water solubility index than non-encapsulated flour. There were no significant differences in anthocyanin content between encapsulated and non-encapsulated flours. However, water absorption index and flavonoids content of encapsulated flours depended on concentrations of ascorbic acid and maltodextrin. In addition, the high concentrations of ascorbic acid and maltodextrin encap- sulated flours had higher glass transition temperature as compared to that of lower concentrations. In respect to morphology, the particles of encapsulated flours with high concentration of ascorbic acid and maltodextrin were more aggregated than those encapsulated with lower concentrations. Therefore, flours encapsulated with 10 g kg 1 ascorbic acid and 30 g kg 1 maltodextrin could be used to enhance the antioxidant activities of functional food ingredients. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Purple-fleshed sweet potatoes have intense purple colour due to the accumulation of anthocyanins (Terahara, Konczak, Ono, Yoshimoto, & Yamakawa, 2004). Purple-fleshed sweet potatoes are good sources of acylated anthocyanins with aromatic acids (Yang & Gadi, 2008). The anthocyanins of purple sweet potato have many biological functions such as scavenging free radicals, anti- mutagenicity, anticarcinogen activity and antihypertensive effect (Oki et al., 2002). Processing the sweet potato into flour increases its storage ability and value. Sweet potato flour can be used as a thick- ener in soup, gravy, fabricated snacks and bakery products (Van Hal, 2000). It can also be used to enhance food products through colour, flavour, natural sweetness and supplemented nutrients. Encapsulation technology has been used in the food industry to provide liquid and solid ingredients as an effective barrier against environmental parameters such as oxygen, light, free radicals etc (Desai & Park, 2005). Bioactive compound could be improved using encapsulation technique which entraps a sensitive ingredient inside a coating material (Saenz, Tapia, Chavez, & Robert, 2009). Spray drying is the most commonly used encapsulation method in the food industry. Encapsulation by spray drier is an economical method for preservation of natural colourants by entrapping the ingredient in a coating material (Cai & Corke, 2000). The most commonly used materials for encapsulation are maltodextrins of different dextrose equivalents. Maltodextrin are water-soluble materials and protect encapsulated ingredient from oxidation. Some studies have explored the use of carrier agents such as maltodextrin and gum arabic to protect sensitive compounds like vitamin C in fruit juice and to increase product stability in acerola powder (Desobry, Netto, & Labuza, 1997; Dib Taxi, De Menezes, Santos, & Grosso, 2003; Righetto & Netto, 2005). A recent study found that maltodextrin can enhance the phenolic and anthocyanin content during processing of purple sweet potato flour (Ahmed, Akter, & Eun, 2009). Encapsulated acidulants that are commer- cially available are adipic acid, ascorbic acid, citric acid, fumaric acid and malic acid (Shahidi & Han, 1993). Ascorbic acid is a water- soluble vitamin, which is regarded as a vitamin supplement to reinforce dietary intake of vitamin C and as an antioxidant, to protect the sensory and nutritive quality of the food itself (Uddin, Hawlader, & Zhu, 2001). Un-encapsulated food acids can react with food ingredients to produce many undesirable effects such as * Corresponding author. Tel.: þ82 62 530 0255; fax: þ82 62 530 2149. E-mail address: jbeun@jnu.ac.kr (J.-B. Eun). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt 0023-6438/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2010.05.014 LWT - Food Science and Technology 43 (2010) 1307e1312